This invention relates generally to the area of a power supply indicator used in conjunction with an electrical device. More particularly, this invention relates to an improved low battery indicator for use, though not exclusively, with a wrist watch paging receiver.
Paging receivers and wrist watches are electrical devices which are powered by battery power supplies. As the battery discharges a paging receiver generates a low battery indication. In many cases, paging receivers continue to operate properly for several days after the low battery indication. It is desirable to enable the user of the paging receiver to expend the total capacity of the battery remaining after the low battery indicator while still providing ample low battery indications in order that a new battery or a battery recharge may be obtained.
With the advent of lower power and smaller paging receivers incorporated together with wrist watch functions, the feasibility of smaller, lower capacity batteries is becoming apparent. Such batteries suffer from irregular performance towards the end of the life of the battery. Current pagers use many types of battery technologies such as nickel-cadmium, alkaline, carbon-zinc, mercury and zinc-air. Each battery technology has different characteristics, particularly towards the end of the life of the battery. Additionally, advances in the battery manufacturing industry are continually improving battery performance. For example, today's alkaline battery has substantially more capacity than the alkaline battery of just two years prior.
Prior art low battery indicators used with pagers have operated simply to display the text "LOW CELL" or "LO CELL", or an annunciator or low battery icon when the battery voltage reaches a predetermined voltage. Still other low battery indicators generate only a short tone burst, which if not heard by the user may go unnoticed. Yet still another low battery indicator generates a continuous alert tone. These prior art low battery indicators provide no indication as to the time since the low battery state has been detected, and further provide no means for determining the battery capacity remaining.
Additionally, in miniature display applications, it is desirable to provide a "LO CELL" indication in the same area used to convey other information. This is particularly true in applications such as digital watches or watches having paging receivers incorporated therein, wherein the display area is very small. The display of a "LO CELL" indication may displace the display of time, date or message information. Thus it is desirable to provide for both the display of low cell information while providing for the display of time, date or message information. Is further desirable to make such a provision in a manner that provides for an indication of the remaining capacity of the battery.